Fluid filters are commonly used in connection with lubrication and fuel supply systems for internal combustion systems as well as hydraulic systems. The filter assures that downstream systems operate properly. Many systems utilize replaceable filter elements such that when the filtration media or device that actually does the filter becomes spent, it can be easily and cost-efficiently replaced without requiring the entire filter assembly being replaced.
However, upon excess buildup of filtered debris, the flow of fluid through the system can become limited which can hinder the operation and potentially damage the downstream system. As such, some filter assemblies have incorporated a fluid bypass that opens upon excess pressure build up. The bypass acts to allow dirty fluid to short-circuit the filter element of the filter assembly when the filter element becomes clogged with contaminants. Although it is not typically preferred to allow dirty fluid to flow through the filter without being filtered, it is more preferable than preventing a sufficient amount of fluid such as lubricating oil or fuel to flow through the system which can result in catastrophic engine failures.
An example of such a fluid filter is disclosed in U.S. Pat. No. 5,770,054 to Wilhelm Ardes. The '054 patent to Ardes includes a filter element with an upper plastic end cap providing a bypass valve seat that seats against a spring biased valve member on a standpipe in a housing. Due to end cap alignment issues and material issues, there are concerns about reliability of sealing, particularly at the valve seat formed integrally into the plastic upper end cap. Further, because the spring biased valve member forms part of the filter base, the spring biased valve member and its biasing mechanism, typically a coil spring, are not replaced when the spent filter element is replaced. Unfortunately, the Applicants have determined that this can result in additional problems. For example, the biasing mechanism can become worn such that the bypass valve will open under pressure that is too low, i.e. before the filter element becomes sufficiently spent.
Also, International Patent Application PCT/US2008/066739, published as WO 2008/157244 to John Hacker illustrates a further filter assembly using a bypass arrangement. In this arrangement, the filter element includes a valve member that interacts with a valve seat formed by the end cap. The valve member is axially biased against the valve member of the Ardes arrangement that forms part of the filter base to bias the valve member toward a closed position. While a portion of the bypass valve, namely the valve member, is replaced at each maintenance interval, the force biasing the valve member again relies on the biasing mechanism provided by the filter base. Thus, this design once again has the perceived downfalls.
The present invention relates to improvements over Ardes and Hacker and the current state of the art in fluid filters that incorporate a fluid bypass.